Current techniques for the screening of breast cancer, as a prerequisite to biopsy for diagnostic evaluation of a potential tumor, include physical breast examination and mammography. These techniques possess a number of limitations, including lack of specificity and accuracy in the diagnosis and, also a lack of cancer stage and prognostic information. This ultimately yields high numbers of false positive diagnoses, and consequently unnecessarily large numbers of surgical biopsies. The rationale behind this proposal is based on two sources of data: 1) Current scientific literature, in which there is growing evidence that individuals with breast cancer and other forms of malignant disease such as prostate cancer, exhibit immune responses that can be detected at the level of altered gene expression in leukocytes circulating in peripheral blood. Quantitation of the mRNA transcripts in leukocytes of a number of individual genes has demonstrated associations between gene expression levels and the presence of a tumor in patients with breast and prostate cancer. 2) Preliminary results from a microarray study investigating gene expression changes in men with prostate cancer. Initial results from this study have been striking; supervised cluster analysis of peripheral leukocyte gene expression data, using transcript level measurements of thousands of genes from eleven prostate cancer patients and seven matched control subjects, resulted in a classification of all the subjects into their correct group. These observations form the basis of the hypothesis and experimental design of this proposed study. Under Specific Aim One, we will collect and process blood from 55 breast cancer patients and 25 healthy control subjects. We will then employ microarray technology to measure simultaneously the expression levels of up to 14,000 genes transcribed in leukocytes derived from the blood of breast cancer patients and control subjects, and employ data analysis algorithms to determine patterns of gene expression specific for each subject group. With this technology we propose to investigate our central hypothesis: that individuals suffering from breast cancer exhibit a conserved pattern of gene expression levels in their peripheral blood leukocytes, which is distinct from the pattern of expression in peripheral blood leukocytes from control subjects. Under Specific Aim Two, we will test the further hypothesis that cancer patients with breast tumors at different histological grades will yield distinct expression signatures that reflect the biological stage and aggressiveness of the tumor, and that can thus be employed to differentiate among tumors at different pathological stages. We believe that the diagnostic technique we propose to develop may ultimately form the basis of a clinical assay that will, with a minimum of patient discomfort, have the capacity to identify women with breast cancer, and also provide important stage-specific information. [unreadable] [unreadable] [unreadable] [unreadable] [unreadable]